intrinsically smart cement-matrix composites topic 5
TRANSCRIPT
Intrinsically smartcement-matrix composites
Topic 5
Reading assignment
Chung, Composite Materials, Ch. 13. No. 130, under “Publications – cement” in
website http://www.wings.buffalo.edu/academic/department/eng/mae/cmrl
Functions
Structural Strain/stress sensing Damage sensing Temperature sensing Electromagnetic interference (EMI) shielding Vibration reduction Self-heating
Applications of strain-stress sensing
Structural vibration controlTraffic monitoringWeighing (including weighing in
motion)Building facility managementSecurity
Strain/stress sensing
PiezoresistivityDirect piezoelectricity
PiezoresistivityChange of electrical resistivity due to
strainGage factor = fractional change in
resistance per unit strain (more than 2)Gage factor up to 700 attained in
carbon fiber reinforced cement
With carbon fiber
Tension
With carbon fiber
Tension
Without carbon fiber
Tension
Applications of damage sensing
Structural health monitoringDamage/microstructural
evolution study
Damage sensing methods
Acoutic emissionElectrical resistivity
measurementOptical fiber sensor
embedment
Resistance measurement methods
Volume resistance (for sensing the damage of a volume)
Surface resistance (for sensing the damage of the surface)
Contact resistance (for sensing the damage of an interface)
Apparent volume resistance (for sensing the damage of an interface between dissimlar materials)
A1 A2 A3 A4
B4B3B2B1
160
40
40
140
20 20 20 2080
Flexure
Dimensions in mm
With carbon fiber
Flexure
Surface resistance at compression side
Surface resistance at tension side
With carbon fiber
Flexure
Through-thickness resistance
With carbon fiber
Flexure
Oblique resistance
With carbon fiber
Flexure
Oblique
Surface –tension
Through-thickness
Surface - compression
Mortar (without fiber) during freeze-thaw cycling
Without freezing
Carbon fiber concrete under repeated
compression
Interface between concrete and steel rebar under cyclic shear
Interface between old and new mortar
under cyclic shear
Interface between unbonded mortar elements
under cyclic compression
Interface between concrete and its carbon fiber epoxy composite
retrofit
Applications of temperature sensing
Thermal controlStructural operation controlHazard monitoring
Temperature sensing methods
ThermocouplesThermistors
Cement-based thermistor
Carbon fiber reinforced cementActivation energy = 0.4 eV
Table 2.2 Resistivity, critical voltage and activation energy of five
types of cement paste.
Activation energy (eV) Formulation Resistivity at 20oC (.m)
Critical voltage
at 20oC (V) Heating Cooling
Plain Silica fume Carbon fibers + silica fume Latex Carbon fibers + latex
(4.87 ± 0.37) x 103
(6.12 ± 0.15) x 103
(1.73 ± 0.08) x 102
(6.99 ± 0.12) x 103
(9.64 ± 0.08) x 102
10.80 ± 0.45
11.60 ± 0.37
8.15 ± 0.34
11.80 ± 0.31
8.76 ± 0.35
0.040 ± 0.006
0.035 ± 0.003
0.390 ± 0.014
0.017 ± 0.001
0.018 ± 0.001
0.122 ± 0.006
0.084 ± 0.004
0.412 ± 0.017
0.025 ± 0.002
0.027 ± 0.002
Cement-based thermocouple
Carbon fiber reinforced cement (p-type)
Steel fiber reinforced cement (n-type)pn-junction70 microvolts/degree C
Thermoelectric cement-based materials
Absolute thermoelectric power tailored by using conductive admixtures
Carbon fiber for p-type behaviorSteel fiber for n-type behavior
Effect of stainless steel fiber (60 micron diameter)
Applications of electrically conducting cement-based materials
EMI shieldingElectrostatic protectionLightning protectionCathodic protectionSelf-heatingLateral guidance in automatic
highways
Lane Lane
(a) (b)
Cement pastes (with 1 vol.% conductive admixture)
Steel fiber (8 microns) 40 ohm.cm Carbon fiber (15 microns) 830 ohm.cm Carbon nanofiber (0.1 micron) 12,000 ohm.cm Graphite powder (0.7 micron) 160,000 ohm.cm Coke powder (less than 75 microns) 38,000 ohm.cm